1. Technical Field of the Invention
This invention relates to bismaleimides. More particularly, this invention relates to bismaleimide derivatives of higher molecular weight polyoxyalkyleneamines. Still more particularly, this invention relates to bismaleimide derivatives of higher molecular weight polyoxyalkyleneamines prepared by reacting a bismaleimide prepared from a low molecular weight oxyethylenediamine with higher molecular weight (&gt;200) polyoxyalkyleneamines to form bis(maleimidoaspartimide) compounds useful in the preparation of polybismaleimides.
These compounds form clear or transparent orange polymers which can be hard or flexible, have a high temperature of decomposition and can be used for matrix resins in composites.
In a second embodiment of this invention aromatic bismaleimide derivatives are prepared by reaction of polyoxyalkyleneamines with commercially available aromatic bismaleimides. These materials are useful in the preparation of homopolymers and copolymers suitable as matrix resins in composites.
2. Prior Art
The preparation of polybismaleimides by polymerization of bismaleimides is known. Bismaleimide polymers are important primarily for their thermal stability, which usually results from aromaticity in the structure. Although the majority of bismaleimides have therefore been prepared from aromatic diamines, aliphatic compounds can also provide benefits in improved processibility, flexibility and solubility. Bismaleimides have, for example, been prepared from alkylene-diamines (J. Appl. Poly. Sci., 29, 891-899 (1984). Here the polymers were prepared by Michael addition with bisnucleophiles instead of by radical addition of the double bonds to each other.
Bismaleimides have also been prepared from JEFFAMINE.RTM. ED-diamines (U.S. Pat. No. 3,951,902). In U.S. Pat. No. 3,951,902, JEFFAMINE.RTM. ED-900, a polycapped polyoxyethyleneamine, is treated with maleic anhydride to form bismaleamic acid which is cyclodehydrated with acetic anhydride. One disadvantage of this procedure is that it involves removal of dimethylformamide, a high-boiling solvent.
In a series of Japanese patents issued to Mitsui Toatsu Chemicals (JP Nos. 82 205,413; 83 40,374; 83 15,515; 83 136,637), bismaleimides were also prepared from diamines such as 4,7-dioxadecane-1,10-diamine (reduction product of cyanoethylated ethylene glycol) and related diamines; these are used with polybutadiene in preparation of copolymers. The maleimide of triethylene glycol monoamine is also reported in one of these patents.
Use of the oxyethylene group to increase flexibility has been effective in some other types of polymers. In J. Macromol. Sci. Chem., A21, 1117-1135 (1984) there is described preparation of "reactive plasticizers" with acetylene endgroups and internal oxyethylene groups.
Stenzenberger, in German Pat. No. 2,127,024 disclosed the preparation of an aliphatic bismaleimide from 2,2,4-trimethylhexane-1,6-diamine and in German Pat. No. 2,165,974 he described its thermal polymerization.
The use of mixtures of polyoxyalkylene bismaleimides (with molecular weights greater than 400) and aromatic bismaleimides in preparation of flexibilized polybismaleimides is disclosed by de Koning in European Patent Application No. 206,383. While the heat distortion temperature fell with increasing amounts of flexibilizing bismaleimide, the elongation and flexure at break both increased as well.
In U.S. Pat. No. 4,237,262, Jones discloses a low temperature curable composition comprising at least one curable polyimide prepolymer formed by heating an aliphatic oxyalkylene bismaleimide with an aromatic polyamine and at least one aromatic bismaleimide and at least one aliphatic epoxy resin. The reaction product provides at least two functional epoxy groups to provide a low temperature curable composition. In U.S. Pat. No. 3,951,902 Jones et al. disclose a compliant polyimide having superior thermal mechanical properties produced by reacting an aromatic bis(furfurylimide) with an aliphatic ether bis(maleimide) via a Diels-Alder reaction. In U.S. Pat. No. 4,116,937, Jones also discloses a resin system prepared by Michael addition of a mixture of oxyalkylene and aromatic bismaleimides to aromatic diamines. The oxyalkylene bismaleimides have molecular weights of at least 750, and the product is a glassy solid at room temperature. In that case the diamine is always aromatic. It is doubtful that products made from an aromatic-containing compound such as this could be water-soluble.
In European patent application No. 191,931, Nagasaki reveals the use of certain oxyalkylene bismaleimides in rubber compositions.
A curable resin composition is disclosed in Jpn. Kokai Tokkyo Koho JP Nos. 58, 136,637 [83,136,637] 13 August 1983 to Mitsui Toatsu Chemicals. The compound contains an aliphatic imide and polybutadiene containing double bonds.
A Japanese Patent to Mitsui Toatsu Chemicals, Inc. (JP No. 58,127,735 [83,127,735] (C1. C08G 73/10), July 29, 1983) discloses heat resistant electrical insulators for printed circuit boards are prepared from mixtures of aliphatic polyether bisimides, aromatic bisimides and diamines.
Polymerization of the bismaleimide of dimer diamine, which also contains a hydrocarbon backbone, is disclosed in U.S. Pat. No. 4,564,663. The product polymer is hard and thermally stable.
An article by White in Ind. Eng. Chem. Prod. Res. Dev. 25, 395-400 discusses the fact that bisimides offer potential for the synthesis of high-molecular-weight, step growth polymers. It is stated they are flanked by two electron-withdrawing carbonyl groups and the electrophilic maleimide carbon-carbon-double bond is especially labile to nucleophilic attack and yields Michael type adducts with both amines and thiols. The paper focuses on the requirements for preparation of these polymeric Michael adducts, with additional emphasis on the effects of the enormous structural variety available within the class in the thermal and physical properties of these new resins.
In the art experimental data are available wherein polymers were synthesized which are structurally related to those formed by nucleophilic or Michael addition of diaminoarenes, but which had more flexible backbones and lower glass transition temperature (Tg). See "Reaction of Diaminoalkanes with Bismaleimides: Synthesis of Some Unusual Polyimides", Journal of Applied Polymer Science, Vol. 29, 891-899 (1984).
Shaw and Kinloch have studied the effects of rubber concentration on the morphology, bulk mechanical and thermal properties and the adhesive strength of the bismaleimide by the addition of various amounts of a carboxyl-terminated butadiene (CTBN) rubber toughening agent, and concluded that surprisingly large amounts of CTBN rubber can be added to substantially improve the fracture resistance of the bismaleimide resin without sacrificing other important properties. (See "Toughened Bismaleimide Adhesives", Int. J. Adhesion, July 1985, pp. 123-127.)
A growing number of applications for polyimides are discussed in the article titled "Premium Performance from Polyimides" in ME, January 1986, p. 14-19.
In U.S. Pat. No. 4,277,582 Mueller discloses water-insoluble hydrophilic copolymers consisting of a hydrophilic polymer of monoolefinic monomers cross-linked with a major amount of a diolefinic non-hydrophilic macromer.
It appears there is a large market for bismaleimides and a good deal of research in the art has been directed toward studying properties of and better methods for producing these compounds. It is believed the polybismaleimide derivatives of the instant invention, particularly those derived from higher molecular weight polyoxyalkyleneamines reacted with bismaleimides of low molecular weight diamines would exhibit advantages including increased flexibility, reduced brittleness, improved low-temperature properties and would be useful as matrix resins in composites.
Advantages of the first embodiment invention include the fact that aromatic amines, which are in many cases known or suspected to be carcinogenic or otherwise toxic, are not used to prepare the materials.
In the second embodiment of the invention monomers are prepared having a polyoxyalkylene backbone and aromatic bismaleimide termination.
The products resulting from the second embodiment would be of particular interest because they are formed from the reaction of two commercially available materials. The method of preparation disclosed is much easier than the direct route, using maleic anhydride. These materials are useful in the preparation of homopolymers and copolymers that may be suitable as matrix resins in composites.